Scale settings for exporting to STL (for 3d printing)
The STL exporter doesn't take Scene Scale into account. Import your STL back into Blender (it will have the same size) and drag Scene Scale up back to 1.0, and you'll see how the cube grows relative to the grid.

1 Blender unit equals 1m, but STL seems to assume 1 unit as 1cm.

If you want 1 unit to be 1mm, set Scale on STL export to 0.1 and Scene Scale to 0.001 to make it match the output scale in viewport.

Note that the STL will be 10x smaller if you re-import it into Blender!